Quantum chemical simulation of the self-trapped hole in α-Al2O3crystals

Atomistic simulations of hole self-trapping in a pure corundum crystal have been undertaken using three different approaches. The inward Jahn-Teller displacement of two O atoms (on which 80% of the hole density is concentrated), accompanied by the outward displacement of the two nearest Al atoms, gives the energetically most favorable configuration, thus suggesting a self-trapped-hole (STH) model analogous to that in alkali halides (${\mathit{V}}_{\mathit{K}}$ center). The optical absorption of STH and three possible kinds of thermally activated hops are discussed in relation to experimental data.